Exhaust purification system and catalyst regeneration method

Abstract

There is provided: a NOx occlusion reduction-type catalyst that is provided in an exhaust passage of an internal combustion engine, occludes NOx in exhaust when the exhaust is in a lean state, and reduces and purifies the occluded NOx when the exhaust is in a rich state; an exhaust injector that is provided in the exhaust passage and is positioned further upstream than the NOx occlusion reduction-type catalyst; a NOx-purging control unit that performs NOx purging of reducing and purifying the NOx occluded in the NOx occlusion reduction-type catalyst by lowering the exhaust to a prescribed target lambda by fuel injection by the exhaust injector; and a NOx-purging-prohibition processing unit that inhibits performance of the NOx purging in a case where the exhaust cannot be lowered to the target lambda even if the fuel injection is performed at a maximum limit injection amount of the exhaust injector.

The invention claimed is: 
     
       1. An exhaust purification system comprising:
 a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of an internal combustion engine, occludes NOx in exhaust when the exhaust is in a lean state, and reduces and purifies the occluded NOx when the exhaust is in a rich state; 
 an exhaust injector that is provided to the exhaust passage, is positioned further upstream than the NOx-occlusion-reduction-type catalyst, and injects fuel into the exhaust passage; and 
 an electronic control unit (ECU), wherein the ECU:
 performs catalyst regeneration processing of reducing and purifying the NOx occluded in the NOx-occlusion-reduction-type catalyst by lowering a lambda value of the exhaust to a predetermined target lambda at least by fuel injection by the exhaust injector; 
 inhibits performance of the catalyst regeneration processing in a case where the lambda value of the exhaust cannot be lowered to the target lambda even if the fuel injection is performed at a maximum limit injection amount of the exhaust injector; and 
 estimates a reachable exhaust lambda based on the maximum limit injection amount of the exhaust injector and inhibits the catalyst regeneration processing by the ECU in a case where the estimated reachable exhaust lambda is greater than the target lambda. 
 
 
     
     
       2. An exhaust purification system comprising:
 a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of an internal combustion engine, occludes NOx in exhaust when the exhaust is in a lean state, and reduces and purifies the occluded NOx when the exhaust is in a rich state; 
 an exhaust injector that is provided to the exhaust passage, is positioned further upstream than the NOx-occlusion-reduction-type catalyst, and injects fuel into the exhaust passage, and 
 a control unit, 
 wherein the control unit operates so as to execute the following processing:
 reducing and purifying the NOx occluded in the NOx-occlusion-reduction-type catalyst by lowering a lambda value of the exhaust to a predetermined target lambda at least by fuel injection by the exhaust injector; 
 inhibiting performance of the catalyst regeneration processing by the control unit in a case where the lambda value of the exhaust cannot be lowered to the target lambda even if the fuel injection is performed at a maximum limit injection amount of the exhaust injector; and 
 estimating a reachable exhaust lambda based on the maximum limit injection amount of the exhaust injector and inhibits the catalyst regeneration processing by the ECU in a case where the estimated reachable exhaust lambda is greater than the target lambda. 
 
 
     
     
       3. A catalyst regeneration method in an exhaust purification system including: an internal combustion engine; a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of the internal combustion engine and occludes NOx in exhaust when the exhaust is in a lean state, and reduces and purifies the occluded NOx when the exhaust is in a rich state; and an exhaust injector that is provided to the exhaust passage, is positioned further upstream than the NOx-occlusion-reduction-type catalyst, and injects fuel into the exhaust passage, the method comprising:
 reducing and purifying the NOx occluded in the NOx-occlusion-reduction-type catalyst by lowering a lambda value of the exhaust to a predetermined target lambda at least by fuel injection by the exhaust injector; 
 inhibiting performance of the catalyst regeneration processing by the control unit in a case where the lambda value of the exhaust cannot be lowered to the target lambda even if the fuel injection is performed at a maximum limit injection amount of the exhaust injector; and 
 estimating a reachable exhaust lambda based on the maximum limit injection amount of the exhaust injector and inhibits the catalyst regeneration processing by the ECU in a case where the estimated reachable exhaust lambda is greater than the target lambda.